Apparatus and method for converting impure ferrous metal to steel

ABSTRACT

Finely divided materials such as burnt lime, iron oxide and fluorspar are entrained in oxygen and blown into the bottom of a converter vessel. A plurality of nozzles are directed through the side of the vessel above the surface of the melt therein. The nozzles project oxygen streams toward the melt to react with hydrogen and carbon monoxide (CO) evolving therefrom thus effecting an exothermic reaction which provides additional heat to the melt which aids in fluidizing the slag and permits charging the vessel with a greater quantity of scrap.

United States Patent Schempp Oct. 1, 1974 [541 APPARATUS AND METHOD FOR 3,208.1 17 9/1965 Goedcckc 75/59 CONVERTING IMPURE FERROUS METAL 3,248,211 4/1966 Klein 1 75/60 T0 STEEL 3,254,987 6/1966 Graef 75/52 3,330,645 7/1967 MOI/1511C! 75/60 1 1 lnvemori Eberhard 191 sburgh, 3,556,773 1/1971 Grenfell 75/51 p 3,706,549 12/1972 Knuppel 75/60 [73] Assignee: Pennsylvania Epgineering Primary ExaminerL. Dewayne Rutledge Corporamn plttsburgh Assistant Examiner-Peter D. Rosenberg [22] Filed: Jan. 4, 1972 Attorney, Agent, or Firm-Fred Wiviott; Ralph G. 1211 Appl. No.2 215,392 Hmenfeldt [57] ABSTRACT [52] U.S. C1. 75/52, 75/60 Finely divided materials such as burnt lime, iron Oxide [51] Int. Cl. C21c 5/34, C21c 5/32 and fluorspar are entrained in Oxygen and blown into [58] Field of Search 75/ 52-60 the bottom of a converter vesSeL A plurality of nozzles are directed through the side of the vessel above the 1 1 References Clted surface of the melt therein. The nozzles project oxy- UNITED STATES PATENTS gen streams toward the melt to react with hydrogen 2,562,813 7/1951 Ogorzaly 75/60 and Carbon monoxide evolving therefrom thus 2,781,256 2/1957 Richards 75/53 effecting an exothermic reaction which provides addi- 2,820,707 1/1958 Walker 1 75/60 tional heat to the melt which aids in fluidizing the slag 2,986,458 5/1961 Johnson 75/52 and permits charging the vessel with a greater quantity 3,034,887 5/1962 Henne.... 75 52 f scrap 3,198,624 8/1965 Be11........ 75/60 3,201,226 8/1965 Spolders 75/59 8 Claims, 2 Drawing Figures APPARATUS AND METHOD FOR CONVER'IENG IMIURE IFERROUS METAL TO STEEL BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for converting impure ferrous metal to steel with a bottomblown converter vessel.

In the recently discovered bottom-blown variation of the basic oxygen method for converting molten pig iron to steel a refractory lined vessel is first charged with hot metal and scrap. Oxygen is then blown through tuyeres in the bottom of the vessel along with finely divided materials which are entrained in the gas. Fluxes such as burnt lime and fluorspar, limestone, desulphurizing and dephosphorizing agents such as calcium cyanate and iron oxide are typical of finely divided materials which may be introduced to the melt in this manner. A hydrocarbon fluid such as propane gas or petroleum oil is also injected into the melt simultaneously with oxygen. The tuyeres are designed so that the hydrocarbon cracks endothermically near the inner tip of the oxygen jet and this cools the superheated melt materials caused by oxidation so they are not so hot to deteriorate the refractory lining at a rapid rate.

The oxygen which is injected through the vessel bottom diffuses through the melt and reacts with various elements therein, notably carbon. This reaction is exothermic and results in the temperature of the molten metal being raised. The carbon and oxygen reaction produces mainly carbon monoxide which evolves from the melt and passes through the slag layer. The hydrocarbon cracks, due to the high temperature which prevails, causing combustible hydrogen to evolve also. The hydrogen and carbon monoxide do not ordinarily burn in the vessel in accordance with past practice because substantially no excess oxygen evolves from the melt.

In the bottom blown process, quantities of finely divided burnt lime, for example, are injected into the melt. Desirably, the lime should react with constituents of the melt such as silicate, phosphorus and sulphur. The reactions are mostly occurring in the melt, and the end products collect on top of the melt because they are of low specific weight. It has been found that typically these end products are in a layer which is in a nonmolten, granular or dry condition. The layer is often not fluidized even at the end of a full oxygen blowing cycle.

In the bottom blown process there is considerable spitting" which is a term used to signify that globules of molten iron are ejected from the melt into the slag layer. When the slag layer is not adequately molten, homogeneous and fluidized, but is dry as described above, these iron globules are captured by the pulverent slag and remain suspended in it. The iron is thus wasted or lost in the slag. By way of example, it has been estimated that about percent of the materials in a melt form slag and that about 50 percent of the slag is iron globules so that about 5 percent of the potential iron or steel yield of a melt is lost in the slag under these unfavorable conditions.

Another disadvantage of the slag being dry or inadequately fluidized is that the slag acts as an insulating layer which tends to inhibit oxidation of some of the iron in the slag to iron oxide. As is known to those skilled in the art of steelmaking, removal of phosphorus from the molten steel depends strongly on the iron oxide content of the slag. Moreover, a slag with relatively high iron oxide content tends to become fluidized sooner and easier because iron oxide acts as a flux which lowers the melting point of the slag. As implied, a fluidized slag would permit the spitted iron globules to sink out of the slag and back into the melt for complete refinement since the specific weight of the iron is about three times that of the slag.

Another disadvantage of the present bottom blown process is the fact that dry slag conditions preclude any further chemical reaction between metal bath and slag, although an excess of slag material favorable is continued sulphur and/or phosphorus removal may be present. A liquid slag would aid with further favorable reactions in addition to the almost instantaneous reactions of the finely divided burnt lime inside the melt volume. In addition, when it is desired to "catch carbon"; that is, when it is desired to stop the process while the carbon content of the melt is high as is required for high carbon steel, the temperature of the liquid steel and the slag is correspondingly low resulting in a solid and nonhomogeneous slag in which the loss of iron is especially great.

SUMMARY OF THE INVENTION A general object of the present invention is to overcome the above-noted disadvantages of the bottom blown steelmaking process as it is currently practiced and to produce some additional advantages as well.

In accordance with the invention, a converter vessel is equipped with a plurality of nozzles that project streams of oxygen from the sides of the vessel, at a small angle with respect to horizontal, into the slag layer and toward the surface of the melt. The oxygen reacts with the carbon monoxide (CO) and hydrogen (H which evolves from the surface of the melt. This is an exothermic reaction which produces more heat in the vessel and causes the slag to become molten and fluidized sooner so that the globules of molten iron which are spit or ejected from the melt will sink out of the slag back into the melt, thus increasing the steel yield significantly. MOreover, the appreciable quantity of additional heat which is thus made available makes it possible for more scrap to be charged in the vessel with the hot metal. It now becomes a certainty that an improved heat balance in favor of larger cold scrap quantities charged will result. Another benefit of the additional heat, besides earlier fluidization or melting of the slag, is the production of more iron oxide in the slag for accelerating removal of phosphorus for reasons given above. In addition, the slag containing di-calcium silicate, which is especially dry at the low temperatures existing at the time it is desired to catch carbon at a high level, is now raised to a high enough temperature very early in the melt process cycle to become liquid and contribute to fluidization of the slag.

Accordingly, objects of this invention are to blow oxygen over the top of the molten metal in a bottom blown steel converter so as to produce more heat and thus enable early fluidization of the slag, a decrease in the loss of metal to the slag and] an increase in the amount of scrap and molten metal that can be processed in asingle batch or heat.

A further object is to enable catching carbon of a heat at a high level without losing an inordinate amount of metal to the slag.

A still further object is to maximize the effectiveness of the finely divided materials which are injected into the metal for removal of undesirable elements such as sulphur and phosphorus therefrom.

Yet another object is to augment stirring of the melt by use of gas projecting nozzles above the surface of the melt.

How the foregoing and other more specific objects are achieved will appear in the'more detailed description of an example of the new method and apparatus which will be set forth shortly hereinafter in reference to the drawing.

DESCRIPTION OF THE DRAWING FIG. l is an elevation view of a converter vessel with the lower part broken away to show the interior thereof and to show how the invention is incorporated; and

FIG. 2 shows one form of fluid cooled nozzle assembly which may be used to direct oxygen toward the molten metal in a converter vessel in accordance with the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. l the converter vessel is designated generally by the numeral 10. The vessel comprises a metal shell 11 whose interior is lined with refractory material 12. The upper end of the vessel has a mouth or opening 113 for allowing evolved gases to escape and to permit discharge of residual slag when the vessel is inverted after its useful molten metal contents have been poured out. The refined molten metal may be discharged through a pouring spout 114 when vessel it) is suitably tilted. The trunnion ring on which the vessel is usually supported for tilting is not shown because tilting supports and associated drive mechanisms are well known and are understood to be present. A water cooled hood I5 is situated over vessel during the refining process to collect evolved gases which include carbon dioxide (CO CO and H The hood connects to an exhaust and gas cleaning system, not shown, by means of an exhaust pipe 16 a fragment of which is shown.

The refractory lined bottom of vessel It) is provided with a plurality of tuyeres 17. These tuyeres are preferably arranged in a circle around the bottom of the vessel and near the outside margin thereof. Extending into each tuyere i7 is a nozzle '18 through which finely divided materials entrained in oxygen or oxygen alone or other gases may be injected into the molten metal within the vessel. The tuyeres I7 and nozzles 18 are all slanted in the same direction so that gas flowing through them at high pressure will tend to cause the melt within the vessel to swirl or rotate and thereby enhance the reaction rate between the oxygen and the carbon and the finely divided materials which diffuse through the melt during a conversion process cycle. The nozzles 18 are connected to and are fed from a header I9 which is preferably a tubular annulus although only one-half thereof is evident in the drawing. The annular header 19 is supplied from a pipe 20 which leads back to a swivel joint, not shown, and from there to a pressure reservoir, not shown, in which finely divided materials such as burnt lime, fluorspar, limestone and any other fluxes or necessary constituents for refining may be entrained in oxygen or other gas.

There is an enclosed chamber 22 encasing the bottom of vessel It) and a pipe 21 extends into this chamber to symbolize that a hydrocarbon gas may be introduced therein and conducted into the melt through tuyeres 17. The upper surface of the melt may be at about the level of the irregular line 23. The slag layer is not depicted but it may vary in its level above metal level 23 or have no distinct interface line. At the beginning of a bottom blown process cycle the melt would consist of molten pig iron and unmelted scrap.

In accordance with the invention, vessel 10 is equipped with one or more of tuyere openings such as -33% in its side wall and above the maximum expected level 23 of the molten metal. Nozzles -39 extend into the tuyere openings 30-34 respectively. The nozzles are at such angle that they project a jet of oxygen at an angle of incidence to the melt of between 3 and 15, preferably, with respect to horizontal or with respect to the surface of the melt but it will be understood that a greater or lesser angle may be used if desired. As shown, the nozzles 35-39 are circumferentially spaced about the periphery of the vessel about an are which is not so great as to permit molten metal to leak out of the side of the vessel when it is tilted horizontally. The tuyere openings may also be installed in two opposite arcuate zones of the periphery. All nozzles are aimed in a direction whereby the oxygen jets from them impart rotation to the melt in the same direction as is imparted by the slanted nozzles 18 in the bottom tuyeres. This stirring action causes the gas and entrained materials diffusing upwardly to mix thoroughly with the melt and thereby effect more intimate contact with the reactive constituents and permit a shorter blowing cycle. It will be understood, however, that the upper set of nozzles 35-39 may be angled counter to the bottom tuyeres and nozzles 17 and 18, respectively, so that an action more in the nature of turbulence rather than swirling will be produced. It should be understood, however, that the side injection nozzles may be directed radially inward and the bottom tuyeres and nozzles may be directed axially if desired rather than to have either set of nozzles angulated. The various nozzles 35-39 are connected to an annular tubular header which encircles vessel 10 exterior and connects with a supply pipe 41 which leads to a swivel joint and a pressure regulated source of oxygen the last two items not being shown. The nozzles 35-39 are preferably-of a type which direct a laminar, nonturbulent or focused stream of oxygen toward the melt. As mentioned above, the oxygen jets oxidize the CO and H evolving from the melt, thus producing heat which accelerates melting or fluidizing of the slag which is in a thick layer on top of the melt.

In FIG. 2 one type of nozzle assembly for use above the melt level 23 is shown. This assembly has a Laval type thermodynamic nozzle 46 directed toward the interior of vessel 10. A nozzle of this type is characterized by producing a concentrated laminar jet of gas. The nozzle 46 is supplied from a feed pipe 47 which would connect with annular header 40 in FIG. 1. The nozzle and pipe are encased in a cylindrical closed jacket 48 which defines a cavity 49 through which a cooling fluid such as water or air may flow. The cooling fluid inlet pipe is marked 50 and the outlet pipe is marked 51. It will be seen that outlet pipe 51 extends deeply into cavity 49 so that the end of the pipe will draw in coolant when it is hottest. The jacket 48 may have a flange 52 for fastening the nozzle assembly to the vessel shell 11 so that the nozzle 46 will be properly angulated to direct a stream of oxygen tangential to the molten metal both in the vessel. Circumferentially spaced feet 53 are provided to further support and align the nozzle assemblies in the side wall tuyeres.

The above-described nozzle assembly is exemplary but not exclusive of the types which may be used. For instance, the nozzles may be simple straight pipes or tubes which project diverging jets or streams of oxygen toward the melt to effect combustion of CO and H at the melt surface and immediately above in the slag. The side nozzles may be water or gas cooled as desired. The side nozzles and tuyeres may be analogous in construction to those which are used in the bottom of the vessel or they may be variously constructed as those skilled in the art of steelmaking will perceive.

The side tuyeres may also be used to inject finely divided iron oxide such as mill scale or roll scale into the slag layer along with oxygen in a manner analogous to that in which finely divided materials are injected into the bottom of the converter vessel. The injection of additional iron oxide has the effect explained above of increasing fluxing, lowering the melting temperature of the slag, fluidizing it sooner and ultimately aiding phosphorus removal as well as enabling spitting metal globules to sink from the slag back into the melt.

The amount of oxygen delivered by the side nozzles above the melt depends on a number of variables including the vessel size, the desired refining cycle duration and the rate at which oxygen is injected in the bottom tuyeres. Generally, however, the total volume of oxygen blown with the side nozzles will amount to about 5 to percent of the oxygen which is blown by the bottom tuyeres during converting a batch of molten to steel.

I claim:

1. A method of converting molten ferrous metal to steel comprising the steps of:

a. holding a quantity of molten metal in a refractory lined metallurgical vessel,

b. injecting oxygen through the lining of said vessel and below the surface of the molten metal so that the oxygen permeates the molten metal and reacts exothermically with carbon in the metal to produce heat and at least carbon monoxide gas which evolves from the upper surface of said molten metal, and

c. injecting hydrocarbon fluid through the lining of said vessel and in surrounding relation to said oxygen, said hydrocarbon decomposing to provide hydrogen which evolves from the surface of said metal,

. simultaneously injecting oxygen through the lining of said vessel at a first point above the upper surface of the molten metal and in close proximity thereto to effect the combustion of at least some of the carbon monoxide and hydrogen for producing additional heat within the vessel, thereby fluidizing slag which is above the surface of the molten metal,

e. and removing gases from said vessel at a point adjacent the upper end thereof.

2. The method set forth in claim ll including the step a. injecting a hydrocarbon fluid into the vessel below the surface of the molten metal simultaneously with injecting oxygen below the surface of the molten metal as aforesaid, the said hydrocarbon decomposing and producing hydrogen which evolves from the surface of the molten metal,

b. the oxygen which is injected above the surface of the molten metal reacting exothermically with the hydrogen to produce additional heat within the vessel.

3. The method set forth in claim ll including the step a. injecting iron oxide into the vessel during at least part of the time during which oxygen is being injected above the surface of the molten metal, said iron oxide being injected into the slag formed on the surface of the molten metal to thereby render the slag more fluid so as to enable metal globules ejected from the molten metal to sink from the slag back into the melt and to improve removal of phosphorus from the melt.

4. The method set forth in claim 1 and a. injecting the oxygen above the surface of the molten metal at an acute angle with respect to said surface to thereby effect stirring of the slag and molten metal.

5. The method set forth in claim 4 and a. injecting the oxygen below the surface of the melt in a direction opposed to that of the motion of said metal resulting from the injection of oxygen above said surface to produce turbulence in the slag and molten metal.

6. The method set forth in claim 4 wherein:

a. injecting the oxygen below the surface of the melt in substantially the same direction as that of the motion of the metal resulting from the injection of oxygen below the surface of molten metal.

7. The method set forth in claim ll wherein:

a. the oxygen injected into the vessel above the molten metal amounts to about 5 to 20 percent of the oxygen which is injected from below the surface of the molten metal during a process cycle.

8. The method set forth in claim 1 and including the step of injecting a finely divided lime containing material into the molten metal and beneath the surface thereof for forming a slag on the upper surface of said metal.

a a :e:

mvm m1 STATES PATENQQFFICE] 1 CERTIFICATE-OE, CORRECTI Patent No. 017 out d October 1, 1974 lnventofls) Eberhard G. Schempp It is ceftified that errorappearsdfi the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 5, column 6, lihe 35', after "the" cancel "melt" and subs-ti cu te -molten metal- Claim 6, column line 4 1, after ,"t he cancel "melt" substitute "molten metal- Signed and sealed this 7th day of Janoary l975.

(SEAL) Attest:

c. MARSHALL DANN Commissioner of Patents MCCOY M. GIBSON JR. Attesting Officerv FORM PO-IOSO (IO-69) Notice of Adverse Decision in Interference In Interference N 0. 99,282, involving Patent N 0'. 3,889,017, E. G. Schempp, APPARATUS AND METHOD FOR CONVERTING IMPURE FER- ROUS METAL TO STEEL, final judgment adverse to th patentee was rendered June 16, 197 7 as to claims 1, 2, 4, 5, 7 and 8.

[Official Gazette September 20, 1.977.] 

1. A METHOD OF CONVERTING MOLTEN FERROUS METAL TO STEEL COMPRISING THE STEP OF: A. HOLDING A QUANTITY OF MOLTEN METAL IN A REFRACTORY LINED METALLURGICAL VESSEL, B. INJECTING OXYGEN THROUGH THE LINING OF SAID VESSEL AND BELOW THE SURFACE OF THE MOLTEN METAL SO THAT THE OXYGEN PERMEATES THE MOLTEN METAL AND REACTS EXOTHERMICALLY WITH CARBON IN THE METAL TO PRODUCE HEAT AND AT LEAST CARBON MONOXIDE GAS WHICH EVOLVES FROM THE UPPER SURFACE OF SAID MOLTEN METAL, AND C. INJECTING HYDROCARBON FLUID THROUGH THE LINING OF SAID VESSEL AND IN SURROUNDING RELATION TO SAID OXYGEN, SAID HYDROCARBON DECOMPOSING TO PROVIDE HYDROGEN WHICH EVOLVES FROM THE SURFACE OF SAID METAL, D. SIMULTANEOUSLY INJECTING OXYGEN THROUGH THE LINING OF SAID VESSEL AT A FIRST POINT ABOVE THE UPPER SURFACE OF THE MOLTEN METAL AND IN CLOSE PROXIMITY THERETO TO EFFECT THE COMBUSTION OF AT LEAST SOME OF THE CARBON MONOXIDE AND HYDROGEN FOR PRODUCING ADDITIONAL HEAT WITHIN THE VESSEL, THEREBY FLUIDIZING SLAG WHICH IS ABOVE THE SURFACE OF THE MOLTEN METAL, E. AND REMOVING GASES FROM SAID VESSEL AT A POINT ADJACENT THE UPPER END THEREOF.
 2. The method set forth in claim 1 including the step of: a. injecting a hydrocarbon fluid into the vessel below the surface of the molten metal simultaneously with injecting oxygen below the surface of the molten metal as aforesaid, the said hydrocarbon decomposing and producing hydrogen which evolves from the surface of the molten metal, b. the oxygen which is injected above the surface of the molten metal reacting exothermically with the hydrogen to produce additional heat within the vessel.
 3. The method set forth in claim 1 including the step of: a. injecting iron oxide into the vessel during at least part of the time during which oxygen is being injected above the surface of the molten metal, said iron oxide being injected into the slag formed on the surface of the molten metal to thereby render the slag more fluid so as to enable metal globules ejected from the molten metal to sink from the slag back into the melt and to improve removal of phosphorus from the melt.
 4. The method set forth in claim 1 and a. injecting the oxygen above the surface of the molten metal at an acute angle with respect to said surface to thereby effect stirring of the slag and molten metal.
 5. The method set forth in claim 4 and a. injecting the oxygen below the surface of the melt in a direction opposed to that of the motion of said metal resulting from the injection of oxygen above said surface to produce turbulence in the slag and molten metal.
 6. The method set forth in claim 4 wherein: a. injecting the oxygen below the surface of the melt in substantially the same direction as that of the motion of the metal resulting from the injection of oxygen below the surface of molten metal.
 7. The method set forth in claim 1 wherein: a. the oxygen injected into the vessel above the molten metal amounts to about 5 to 20 percent of the oxygen which is injected from below the surface of the molten metal During a process cycle.
 8. The method set forth in claim 1 and including the step of injecting a finely divided lime containing material into the molten metal and beneath the surface thereof for forming a slag on the upper surface of said metal. 